The invention relates to adjustable seats for cycles, with both horizontal and vertical supports, which have means for bearing various accessories such as backpacks, baby carriers and bulk containers. The seat of the invention uniquely combines means for adjusting seat position for the rider longitudinally and means for carrying accessory equipment. The vertical backrest of the seat not only affords comfort for the user of any cycle but also affords a thrust surface for the bicycle rider to deliver power more efficiently to the pedals. The vertical backrest also affords means for securing various loads to the seat without interfering with the front-to-rear adjustability of the seat for the rider's comfort. It is therefore an object of the invention to provide a seat, for cycles that have both seat frame and frame post, that has both seat and backrest portions with the backrest portion supporting the rider and various accessories. A further object of the invention is to provide such a seat which is adjustable longitudinally of the cycle without interfering with the attachment of accessories.